Ukraine's top military commander promised an “adequate response” after seven Ukrainian soldiers were killed and 14 injured in the past 24 hours in fighting with Russian-backed separatists, controlling the country’s breakaway far east.

As reported by Censor.NET citing the article by Kyiv correspondent for The Financial Times Roman Olearchyk, the battles mark one of the bloodiest days of fighting this year, as an uptick in the daily shelling and gunfire threatens to reignite full-scale fighting in a smouldering 26-month conflict that has claimed nearly 10,000 lives.

The heightened hostilities are also a stark reminder that while last year's internationally brokered peace accord succeeded in reducing the fighting from peak 2014 levels, the so-called Minsk agreements have failed to deliver a lasting cease-fire or progress on reintegrating the war-torn east with the rest of Ukraine.

"My soul hurts for each life of our soldiers sacrificed for Ukraine... there will be an adequate response," Viktor Muzhenko, the head of Ukraine's armed forces, pledged on Tuesday.

"The armed forces of Ukraine are conducting a systemic build-up of artillery fire," Eduard Basurin, "deputy defense minister" for the Donetsk-based separatists, said on Tuesday.

Ukraine officials said their opponents were stoking the hostilities by stepping up attacks along front lines in the Donetsk and Luhansk regions.

Speaking on television late on Monday, Yevhen Marchuk, a former intelligence chief and Kyiv representative in the Minsk peace talks, said Russia continued to supply arms and fighters to the region and that combined Russian and separatist forces had more tanks than many European countries combined.

Briefing journalists last Friday, Alexander Hug, deputy head of a cease-fire monitoring mission from the Organisation for Security and Co-operation in Europe, urged both sides to pull back, warning that "many of the proscribed weapons we see are situated very close to residential areas."

Noting that while both sides in the conflict claim they are adhering to the Minsk commitments, including withdrawal of all heavy weapons, this was "simply not true", he said.

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